The invention relates to a scroll-conveyor centrifuge for separating a suspension into at least a liquid phase and solid material which deposits, through centrifugal force, on the interior bowl surface facing the helix or scroll and which is conveyed along that inner surface of the bowl to the solid material outlet located in one axial end portion of the bowl by means of the helix rotating at a relatively small differential rate with respect to the bowl, said end portion of the bowl being of conically-diminishing dimension, and the inner surface of the bowl being provided with a texturing which impedes movement of the solid material in a direction circumferential to the bowl.
The solid material which deposits due to the centrifugal force on the interior surface of the bowl during operation of the centrifuge is to be conveyed by the helix to the solid material discharge openings in the casing by the shortest possible path, especially in order to keep down friction and wear. Due to the differential movement between helix and bowl, the solid material appearing between the interior bowl surface and the helix has the tendency to be conveyed along the interior surface of the bowl with a movement component having a circumferential orientation, thereby defining a generally spiral-shaped path leading to the solid material discharge openings. To prevent this, and to convey the solid material as much as possible in the axial direction of the centrifuge bowl, one has previously provided the interior surface of the bowl with grooves, or ridges, or attached lands in order to enhance the reluctance of the solid material to move in the circumferential direction of the bowl on its interior surface. The frictional wear on the helix is counteracted by armoring the outer portions of the helix turns, e.g. by coating them with ceramic powder, tungsten carbide, or the like, the coating surface being made smooth after application, in order to keep the frictional resistance of the solid material at the helix turns as low as possible. Such armor coatings have also been provided in the area of the above-mentioned groove or ridge formations on the interior surface of the bowl. By so shaping the inner surface of the casing in its axial direction, one has previously endeavored to form a protective sedimentary layer intended to counteract the wear and tear on the highly stressed interior surface of the casing bowl caused by displacement of the solid material by the helix.
The forming of grooves, ridges, or lands upon the interior wall of the bowl demands rather costly processing.